Wolbachia strengthens the match between premating and early postmating isolation in spider mites

Endosymbiotic reproductive manipulators are widely studied as sources of postzygotic isolation in arthropods, but their effect on prezygotic isolation between genetically differentiated populations has garnered less attention. We tested this using two partially isolated populations of the red and green color forms of Tetranychus urticae, either uninfected or infected with different Wolbachia strains, one inducing cytoplasmic incompatibility and the other not. We first investigated male and female preferences and found that, in absence of infection, females were not choosy, but all males preferred red-form females. Wolbachia effects were more subtle, with only the cytoplasmic incompatibility-inducing strain slightly strengthening color-form-based preferences. We then performed a double-mating experiment to test how incompatible matings affect subsequent mating behavior and offspring production as compared to compatible matings. Females mated with an incompatible male (infected and/or heterotypic) were more attractive and/or receptive to subsequent (compatible) matings, although analyses of offspring production revealed no clear benefit for this remating behavior (i.e., apparently unaltered first male sperm precedence). Finally, by computing the relative contributions of each reproductive barrier to total isolation, we showed that premating isolation matches both host-associated and Wolbachia-induced postmating isolation, suggesting that Wolbachia could contribute to reproductive isolation in this system.